The method and apparatus disclosed herein are essentially an improvement to the method and apparatus for winding ring-shaped articles disclosed in U.S. Pat. Nos. 3,732,901 and 3,985,310 to Kent, et al, which are incorporated herein by reference.
These patents disclose a method and an apparatus for winding wire strands onto toroidal cores. The apparatus includes a feed mechanism that draws a length of wire from a source spool and feeds it through a feed tube into a radially inwardly facing circular channel. Two pairs of compliant circulating rollers are positioned on opposite sides of the channel to grip the wire and advance it to form a first loop. After the first loop is formed, the leading end of the wire continues to hug the channel's radial boundary as subsequent loops are accumulated inside the first loop during wire feeding.
In the Kent apparatus, a gap is provided in the radial boundary of the channel for receiving a toroidal core, with the core's central aperture aligned with the gap so that the circulating wire passes through the aperture. The upper and lower boundaries of the channel are closely spaced to maintain the loops in a single flat concentric layer as the loops accumulate and are circulated. When sufficient wire has been fed, the feeding is stopped, but the circulation of the loops continues, tightly winding a turn of wire onto the core for each complete circulation of the loops in the channel. Two or more wires can be wound onto a core at the same time with the prior patented Kent apparatus.
Although effective, the Kent apparatus has limited reliability when pushed beyond its useful capacity. It is a complex machine of small scale for manufacturing miniature electronic components; it must operate at a high speed to provide cost-effective manufacturing; the fine wire used is highly susceptible to jamming and buckling, which disable the machine until a skilled technician can correct the problem. These reliability problems prevent the existing machine from being used for manufacturing cores having a large number of wire turns. The existing machine has a circulating channel diameter of 21/2 inches, with a capacity of three feet of wire. When greater lengths are loaded, the wire typically jams in the circulating chamber, which can only reliably contain about five loops of wire. This prevents the prior apparatus from being used to manufacture the many wire wound core products of larger size that are currently manufactured by other methods.
An analysis of this problem has revealed that these functional limitations of the prior art apparatus arise from a number of different structural limitations:
A first limitation of the prior art apparatus is that slightly damaged or dented wire may cause a jam in the machine. If a dent occurs in the leading portion of the wire, it is particularly likely to snag or catch in the machine to cause a jam. The prior art feeding mechanism uses a frictional driven roller to draw the wire from a source spool. The driven roller does not provide sufficient tension to draw the wire through a conventional wire straightener to eliminate kinks. The lack of a wire straightener also prevents the use of wire source spools having a smaller diameter than the circulating channel, because the natural curvature of the wire would cause the leading end of the wire to bend inward from the radial boundary of the channel rather than to hug the wall, as is required for successful operation of the machine.
A second limitation of the prior art apparatus is that each circulating roller pair consists of a driven roller and an idler. This results in an imbalanced driving force acting on the wire, which permits inconsistent and unpredictable slippage between the rollers and the wire. Consequently, the wire loops tend to be deflected out of a flat circular path, causing jamming.
A third limitation of the prior art apparatus is that the circulated wire loops are not advanced at precisely the same rate by the opposite pairs of circulating rollers. This can cause the wire to buckle or bunch between the rollers on one side of the channel and to be pulled excessively tight on the other side of the channel. Furthermore, even if the opposite pairs are turned at precisely the same rate, the conical rubber rollers have slightly unpredictable properties which cause errors to accumulate, especially as the number of wire loops in the channel increases.
A fourth limitation of the prior art apparatus is found in a portion of the circulating channel adjacent to the circulating rollers. The upper and lower boundaries of the channel are spaced apart by a width sufficient to permit the wire loops to circulate without excessive resistance. However, this width can be too wide to restrict unwanted deflection of the wire at the circulating rollers. As the leading end of the wire exits a circulating roller pair, there is a tendency for the adjacent loops to attempt to ride over one another, causing the wire to jam. This is increasingly a problem as loops accumulate, and particularly when the leading end of the wire passes through the circulating roller and must push the adjacent inner loops inwardly. Narrowing the channel width to solve this problem only creates a friction problem that impairs circulation of the wire loops.
A fifth limitation of the prior art apparatus is that the feed tube exit is fixed at a position adjacent to the circulating channel radial boundary, which prevents a large number of wire loops from being accumulated in the chamber. The position is a compromise between larger capacity and reliable entry of the wire. The feed tube exit must be positioned sufficiently close to the channel boundary to permit the wire smoothly to contact the radial boundary in a nearly tangential relationship to avoid entry jams. However, this prevents the width of the accumulated bundle of wire loops from exceeding the distance between the tube exit and the channel radial boundary, because the tube exit must remain inward of the innermost loop for feeding to continue.
A sixth limitation of the prior art apparatus is that the wire cutter, which cuts the wire after each core is wound, requires frequent and expensive replacement. The cutter is a cylindrical shear that is sized to fit closely within a cylindrical cutter block bore. As the cutter wears, the fit loosens. Consequently, a dull cutter creates a burr on the leading end of the wire segment instead of cutting it cleanly. Such a burr is likely to catch on a surface of the channel and cause a wire jam. As this problem develops, the cutter must be replaced.